Certain fistula creating tools include a single nitinol wire shaped into a coil (spring) having two distinct portions—an inner coil and a fin coil. In one application, half of the inner coil portion is deployed into the common bile duct (CBD) and the other half is deployed into the duodenum (DD). The compression between the two coil halves compresses the CBD and DD membranes together, stopping blood flow, resulting in tissue necrosis and eventually the creation of a permanent fistula allowing bile juice from the liver to drain into the duodenum. The fin coil portion of the implant (attached to the inner coil) is deployed into the DD and presses against the DD wall. After the creation of the permanent fistula from tissue necrosis the fin coil ejects the entire implant into the DD for expulsion by the body.
In order to create the required push force between the inner coil and the fin coil, the entire implant needs to be reversed (inside out) to locate the fin coil over the inner coil. This process is very expensive and time consuming to perform using standard shape setting processes.
Also, before deployment into the body the fastening tool is loaded into the lumen of the delivery device (e.g., needle). In order to fit inside the needle the implant is forced to uncoil (flatten) into a “straight” wire which causes the implants distal end (the end coming out of the needle first) to “push” against the needle's inner lumen and generate high friction forces during deployment, thus causing difficulty during deployment. To minimize this friction the implant's distal end could be machined round. However, this must be done after shape setting which would be very expensive and time consuming with a high risk of causing damage to the coil.